Call up BMW district manager. Make sure they know what this dealer has done. Make it clear to district manager this was a car that you intended to keep for collector value in future, and that this value is now in jeporady - depending on the extent of the damage.

If you have lease car, this is not as straight forward to argue. Regardless, let the district manager know what has happened and what he thinks should be the compensation. If he doesn't resond in a "yes sir" style, take your complaint to higher level at BMW. Your owners manual will tell you the numbers to call.